Reset draw modifiers after flushing

bug:8401910

This avoids leaving the renderer in a state with stale pointers (to,
e.g., shaders or color filters)

Change-Id: Idf8b63657041352e70e34e91ea416fe4385d4bc2
diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index e6c636c..3aa9975 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -274,6 +274,7 @@
 
     SkPaint* filterPaint(SkPaint* paint, bool alwaysCopy = false);
 
+    void resetDrawModifiers();
     bool storeDisplayState(DeferredDisplayState& state, int stateDeferFlags);
     void restoreDisplayState(const DeferredDisplayState& state, int stateDeferFlags);